Vent cap assembly



Jan. 2, 1968 P. w. FAIR ETAL 3,361,051

VENT CAP ASSEMBLY Filed March 23, 1966 2 Sheets-Sheet 1 NVENTORS PAUL W. #AIR & CLINTON W. FRAIM ATTORNEYS Jan. 2, 1968 P. w. FAIR ETAL 3,361,051

VENT CAP ASSEMBLY Filed March 28. 1966 2 SheetsSheet 2 PAUL wi 1%? CLINTON W. FRAIM ATTORNEYS United States Patent 3,361,051 VENT CAP ASSEMBLY Paul W. Fair, Lansing, and Clinton, W. Fraim, Stnrgis, Mich, assignors to Motor Wheel Corporation, Lansing, Mich, a corporation of Ohio Filed Mar. 28, 1966, Sat. No. 538,066 7 Claims. (Cl. 98-58) This invention relates to ventilating caps for use on the upper end of vertical concentric flues.

It is an object of the present invention to provide an improved vent cap adapted for easy installation on the dual flue intake and outlet of a sealed combustion heating system and operable to provide a balanced condition or pressure zone under any wind condition for admitting combustion air to and expelling flue products from the sealed combustion system to thereby neutralize the undesirable effects of wind conditions on flue outlet and inlet pressures, and also capable of preventing entrance of rain or condensate water into the flue.

Another object of the invention is to provide a vent cap of the above character which is of simplified and economical construction.

Other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevational view of a flue cap constructed in accordance with a preferred example of the present invention, the right half of this view being taken in vertical center section.

FIG. 2 is a top plan view of the flue cap of FIG. 1 but on a reduced scale.

FIG. 3 is a horizontal section taken on the line 3-3 of FIG. 1.

FIG. 4 is a horizontal section taken on the line 44 of FIG. 1.

Referring to FIG. 1, the flue cap assembly of the present invention is particularly adapted for telescopic installation on the upper ends of the conventional concentrically arranged outlet and inlet flue pipes 6 and 8 of a sealed combustion heater or furnace and comprises an inner cylindrical duct 12 concentrically disposed within and spaced from an outer cylindrical duct 14. The lower end of duct 12 is enlarged at a shoulder 16 and then extends downwardly beyond the lower end of duct 14 to facilitate assembly. Duct 12 is slipped onto the upper end of flue pipe 6 as far as the shoulder, and the outer duct 14 slips into the upper end of pipe 8. This particular overlapping arrangement of the ducts 12 and 14 relative to pipes 6 and. 8 respectively provides less restriction to gas flow in each duct across the telescopic joint. Duct 14 extends through a suitable opening in the roof structure 22 and serves as an atmospheric intake for combustion air which is conducted via the annular duct between pipes 6 and 8 to the combustion chamber of the furnace. Duct 12 serves as an outlet to atmosphere for combustion products conducted thereto from the combustion chamber via pape 6. An apertured horizontal plate 24 slips onto duct 14 and is spot welded at an upright flange 26 thereof to the side of duct 14 to provide a watertight joint therebetween. Plate 24 seats on the upper side of roof structure 22 and is preferably sealed thereto by caulking or suitable sealants to form a watertight barrier around the flue opening of the roof.

The upper cover and baflle structure of cap 10 includes a horizontal bottom wall 28 in the form of a flat sheet metal annulus having inner and outer peripheral flanges 3t) and 32, flange 30 being spot welded to the outer side of duct 14 at a point spaced above plate 24 and below the upper end 34 of duct 14. Wall 28 supports a cylindrical side wall 36 which slips onto and is spot welded Patented Jan. 2, 1968 along its lower edge to flange 32. Wall 36 is concentric with ducts 12 and 14 and extends axially upwardly from wall 28 beyond the upper end 34 of duct 14 and terminates slightly below the plane of the upper end 38 of duct 12. An imperforate circular cover 40, having an upwardly domed portion 42, a flat central portion 44, a flat margin or base portion 45 and a flange 45 dependent from its outer periphery, is adapted to slip over the upper edge of the side wall 36 and is affixed thereto by spot welds along flange 45. Cover 4h provides an imperforate rain and wind shield over the upper ends of ducts 12 and 14. The dome formed by portions 42 and 44 provides an interior annular chamber 46 over the open upper end 38 of duct 12 for receiving the products of combustion therefrom and diverting them downwardly and outwardly in a fountain-like flow as indicated by the arrows in FIG. 1.

A horizontal annular bafile 48 is spot welded along an upright inner flange 50 thereof to the upper end of duct 12. Baflie 48 extends outwardly toward and terminates about /2 inch from the fiat horizontal base portion 45 of cover 40 to thereby form a bottom wall of chamber 46, the space between baflle 48 and portion 45 defining an annular outlet 52. from chamber 46. An intermediate annular baflie 54 having an upright inner flange 56 spot welded to duct 12 extends outwardly therefrom to the inner periphery of side wall 36 and is positioned about of an inch above the upper end 34 of duct 14. Baflie 54 carries an annular baffle 58 which i generally S-shaped in radial cross section and has an upper horizontal flange 60 spot welded to the underside of baffle 54 about midway between duct 14 and side wall 36. The lower flange 62 of battle 58 extends horizontally inwardly and terminates about /2 inch from duct 14 to provide an annular opening 64 therebetween. An annular angle section baflie 66 is positioned directly above opening 64 with its horizontal flange flush with the upper edge 34 of duct 14, the vertical flange of baffle 66 being spot welded to the duct. Another annular bathe 70 is in the form of a flat ring resting on vanes 82 and has several turned up retainer tabs 72 spaced circumferentially around its outer periphery which bear against the inner surface of wall 36 to hold baffle 70 in place. Bathe 70 extends horizontally inwardly from wall 36 to a point slightly inwardly of base portion 45 of cover 49.

As best seen in the left hand portion of FIG. 1 and in FIGS. 3 and 4, side wall 36 has a series of rectangular openings 76 circumferentially spaced therearound which extend from an upper edge 74 thereof flush with baffle 'iil downwardly to a lower edge 78 which is approximately the same elevation as flange. 62 of baffle 58. One vertical edge of each opening 76 is bent inwardly radially of the cap to form a pair of Wind deflector vanes 82 and 84 respectively disposed above and below intermediate baffle 54, baffle 54 being received in the space between vanes 82 and 84 to thereby supportably interconnect ducts 12 and 14. Vanes 32 and 84 both have the same radial dimension, about /2inch, and vane 84 terminates at its inner edge somewhat short of midway between baffle 58 and wall 36. Openings 76 are preferably twelve in number and are circumferentially about four times as wide as the intervening vertical strips 86 of wall 36. Openings '76 thus form exhaust ports for discharging products of gaseous products of combustion from the upper chamber 86, formed between ports 48, 54, 12 and 36, back to the atmosphere and form intake ports for admitting fresh air from the atmosphere into the lower chamber 88 formed between ports '28, 54, 36, 58 and 14. Any water collected in chamber 86 as a result of condensation or entrance of rain through ports 76 is collected on intermediate baflle 54 and drains over the outer edge thereof via the space 90 between the outer edge of baffle 54 and band 80.

Similarly water collecting in lower chamber 38 drains onto bottom wall 28 and is drained therefrom by one or more drain holes 92 provided in wall 28 (FIGS. 1 and 4).

In operation hot fiue gases emitted from the upper end 38 of duct 12 are deflected radially outwardly by the flat central portion 44 of cover 4% and then travel downwardly through opening 52 into chamber 86, the gases being deflected slightly inwardly by baffle '70 on their way to the discharge ports formed by the upper half of openings '76. The gaseous products of combustion thus must travel a downwardly directed tortuous path, and under certain conditions a subsequent circular path, before exiting to atmosphere through the side of cap 1!). Similarly, fresh air for supporting combustion is drawn into chamber 88 via the lower halves of openings 76, and then must travel upwardly through opening 64, thence outwardly around the outer edge of flange 65 and thence inwardly under baffle 54 into the open upper end of the outer duct 14. The fresh air drawn into the combustion system and the flue products discharged from the combustion system, due to their proximity at the point of communication with outside atmosphere, are subjected to like pressure variations resulting from sudden wind gusts and down drafts impinging against cap 10. Accordingly, such outside variations do not induce internal pressure differentials within the combustion system.

Due to the annular shape of chambers 86 and 88 and the vanes 82 and 84 extending radially therein, wind and flue gases tend to commingle and circulate in one circumferential direction in the upper chamber 86. Likewise, wind and intake air circulate in chamber 88. This action is best seen in FIGS. 3 and 4 wherein it will be noted that wind impinging against the roof cap and flowing exteriorly from right to left as viewed in FIGS. 3 and 4 induces a circular flow in each chamber, herein shown to be generally counterclockwise. Although vanes 82 may be angled slightly away from their radial disposition to further promote circular flow in the direction of the angulation, such is not necessary to produce circular flow in chambers 86 and 88. Although Wind stream air currents do enter these chambers on one side of the cap and leave on the other side, they do so without any excessive pressure drop en route. If the velocity of such air currents is fairly high, air flowing around the outside of the cap tends to create a low pressure region on the leeward side of the cap. However, in the leeward interior region Where the air flowing through the annular chambers changes directions sharply before exiting through openings 76 on the leeward side, there is an increased resistance to flow. As a result, most of the pressure drop experienced by the air traveling through the cap is concentrated in the Zone between the point where the direction of flow changes near the exit openings and the outside region of low pressure on the leeward side of the cap, this pressure drop region being remote from and ineffective upon the pressure differential in ducts l2 and 14. In addition, when the wind velocity increases from a zero value, the pressure drop incurred by air flowing through chambers 86 and 88 increases very slowly relative to the increase in pressure drop in the aforementioned Zone. This has the effect of limiting negative pressure inside the cap and thus limiting updrafts to an acceptable value.

Cover 49 deflects gases emitted from duct 12 downwardly into chamber 86 in a fountain-like path. This feature allows the use of the imperforate flue pipe 12 while still providing a low resistance path via chamber 86 and openings 76 for flue gases to escape from the flue pipe. When air currents are present, the flue gases join the circular air flow in chamber 86 and flow out the leeward side of the cap. When there are no air currents, flue gases escape from all of the openings 76. Similar action occurs in lower chamber 88 with respect to the intake or fresh air for the combustion. Duct 12 thus acts as a vertical baffle for the upper chamber 86 which isolates the flow of flue gases traveling upwardly therein from the horizontal wind stream flowing through chamber 86. Duct 14 also serves a similar function in chamber 88. In addition, cap 40 and wall 36 prevent the wind stream from entering the upper ends of the flue pipes, thus acting in a positive manner to minimize down drafts.

A further advantage of cap 10 is the economizer effect obtained by the heat exchange relationship between ducts 12 and 14 due to the conduction of heat outwardly via the sheet metal of duct 12, and heat conduction between chambers 36 and 88 through *baffle 54. Thus fresh air is preheated on its Way to the combustion chamber and exiting flue gases are cooled before being discharged to atmosphere.

Separation of the gaseous products of combustion from the incoming fresh air is assured by baffle 54 and the vertical separation of chambers 86 and 88 and their respective ports provided by band 80.

From the foregoing description, it will now be apparent that the flue cap of the invention provides a combined outlet and inlet duct particularly well adapted for installation on roofs of mobile homes or the like to serve as a wind and rain shield for the upper end of the upright concentric ducts associated with a sealed combustion heater of either the gas or oil fired type. The superim osed annular vaned chambers 86 and 8S and the baflles disposed therein, plus the position of these chambers relative to the upper ends 34 and 38 of ducts 14 and 12, cooperate to provide a tortuous path and wind diverting bafile which neutralizes the effects of wind induced pressure variations. This is achieved in a construction employing entirely sheet metal parts of relatively simple configuration readily assembled by spot welding to provide an economical cap assembly.

It is to be understood that the above described vent cap assembly is shown in the appended drawings substantially to scale except that the thickness of the sheet metal is somewhat exaggerated. Although certain departures from the construction shown herein will be obvious to one skilled in the art in view of the present disclosure without thereby departing from the intended scope of the present invention, the particular vent cap design as shown and described herein is preferred and has successfully met standard wind and water tests of the American Gas Association.

We claim:

1. A combined inlet and outlet cap for the upper end of a dual concentric flue duct arrangement comprising a cylindrical outer duct open at both ends, an inner cylindrical duct open at both ends disposed concentrically within said outer duct and extending through the open upper end thereof and terminating at a point spaced thereabove, a bottom wall secured to said outer duct at a point spaced below the open upper end thereof and extending outwardly therefrom, a cylindrical side wall secured to the outer periphery of said bottom wall and disposed concentric with said ducts, an imperforate cover secured to the upper edge of said side wall and having a domed portion spaced above the upper open end of said inner duct and an intermediate annular baflle secured to the outer surface of said inner duct between the upper ends of said inner and outer ducts and extending horizontally outward ly to the inner periphery of said side wall, said inter mediate baflle forming with said inner duct, side wall and cover an annular chamber surrounding said inner duct and communicating via the space beneath said domed portion of said cover with the open upper end of said inner duct, said intermediate baffle forming with said bottom wall, side wall and outer duct a second annular chamber communicating with the open upper end of said outer duct, said side Wall having a series of circumferentially spaced openings therein communicating with said first chamber above said intermediate baffle and with said sec ond chamber below said intermediate baflle.

2. The combination set forth in claim 1 wherein said inner duct has a horizontal baffle secured adjacent its up per end and extending horizontally therefrom radially outwardly toward said cover but terminating short thereof and defining with said cover an annular opening connecting the space beneath said domed portion of said cover with said first chamber.

3. The combination set forth in claim 2 wherein a second bafiie is secured to said side wall and extends horizontally inwardly therefrom above the upper edge of the openings in the side Wall and terminates below said annular opening between said cover and first chamber.

4. The combination set forth in claim 1 further including a first annular baffle secured to and dependent from said intermediate baffie and terminating spaced above said bottom wall and having a flange extending radially inwardly and terminating short of said outer duct and a second annular bafiie secured to the upper end of said outer duct and extending radially outwardly therefrom toward said first bafiie and above said flange thereof.

5. The combination set forth in claim 1 wherein said side Wall has a series of wind deflector vanes bent radially inwardly therefrom adjacent one vertical edge of said openings and extending into said first and second chambers to promote circular flow of air in said chambers.

6. The combination set forth in claim 5 wherein said vanes are slotted intermediate said first and second chambers and said intermediate baffie is received in said slots to support said inner duct on said side wall.

7. The combination set forth in claim 6 wherein a flat ring is disposed in said first chamber adapted to seat on the upper edges of said vanes extending into said first chamber, said ring having a series of circumferentially spaced bent up tabs bearing against the inner surface of .said side Wall above said openings therein, said ring extending radially inwardly from said side wall and terminating beyond the inner edge of said vanes.

References Cited UNITED STATES PATENTS 2,711,683 6/1955 Ryder 98-46 X 2,974,650 3/1961 McCorquodale 9862 X 2,998,764 9/1961 Bedell et al 98-62 3,211,079 10/1965 Carlson 9862 X 3,274,918 9/1966 Stapleton 98-46 ROBERT A. OLEARY, Primary Examiner.

M. A. ANTONAKAS, Assistant Examiner. 

1. A COMBINED INLET AND OUTLET CAP FOR THE UPPER END OF A DUAL CONCENTRIC FLUE DUCT ARRANGEMENT COMPRISING A CYLINDRICAL OUTER DUCT OPEN AT BOTH ENDS, AN INNER CYLINDRICAL DUCT OPEN AT BOTH ENDS DISPOSED CONCENTRICALLY WITHIN SAID OUTER DUCT AND EXTENDING THROUGH THE OPEN UPPER END THEREOF AND TERMINATING AT A POINT SPACED THEREABOVE, A BOTTOM WALL SECURED TO SAID OUTER DUCT AT A POINT SPACED BELOW THE OPEN UPPER END THEREOF AND EXTENDING OUTWARDLY THEREFROM, A CYLINDRICAL SIDE WALL AND DISPOSED CONCENTRIC PERIPHERY OF SAID BOTTOM WALL AND DISPOSED CONCENTRIC WITH SAID DUCTS, AN IMPERFORATE COVER SECURED TO THE UPPER EDGE OF SAID SIDE WALL AND HAVING A DOMED PORTION SPACED ABOVE THE UPPER OPEN END OF SAID INNER DUCT AND AN INTERMEDIATE ANNULAR BAFFLE SECURED TO THE OUTER SURFACE OF SAID INNER DUCT BETWEEN THE UPPER ENDS OF SAID INNER AND OUTER DUCTS AND EXTENDING HORIZONTALLY OUTWARDLY TO THE INNER PERIPHERY OF SAID WALL, SAID INTERMEDIATE BAFFLE FORMING WITH SAID INNER DUCT, SIDE WALL AND COVER AN ANNULAR CHAMBER SURROUNDING SAID INNER DUCT AND COMMUNICATING VIA THE SPACE BENEATH SAID DOMED PORTION OF SAID COVER WITH THE OPEN UPPER END OF SAID INNER DUCT, SAID INTERMEDIATE BAFFLE FORMING WITH SAID BOTTOM WALL, SIDE WALL AND OUTER DUCT A SECOND ANNULAR CHAMBER COMMUNICATING WITH THE OPEN UPPER END OF SAID OUTER DUCT, SAID SIDE WALL HAVING SERIES OF CIRCUMFERENTIALLY SPACED OPENINGS THEREIN COMMUNICATING WITH SAID FIRST CHAMBER ABOVE SAID INTERMEDIATE BAFFLE AND WITH SAID SECOND CHAMBER BELOW SAID INTERMEDIATE BAFFLE. 